When surface water m ditth is below ground 

 water head, n\t pressure of upweltinq qround 

 water moves it mto tt\t ditch throuqh perm- 

 eable layers (Mrvdft, loq layers). Upwellinq 

 water is capable of "liftinq' mucKs in the. 

 ditch and f lowinq around them. Water also 

 flows by qrdWty outof loq layers into ditch. 





Mucks don't qeneraly ^'^^*» \'!^^'\^^ 

 reach the loq layer T>>:>,Ci''l:Y.^X^ 

 elevation and water is ^■^g?<!iwMit*}fe^Jv 

 free to move in and o ut ■ i'i!^.^x!ittio^ '^^ = 





When surface water level is above qround 

 water head, gravity pressure of elevated 

 water pushes water throuqhany sediment 

 permeable enough to permit transmission. 



VND-WATCR HtAO 



■:■',■ 'AJiUirtn. SANDS 



. Little water floivs into sands because 

 .' qravi'ty pushes muck* rJaht aqainst 

 ' permeable areas of the ditch bottom, 

 sealfnq ihtm off. 



Figure 30. The effect of ditches on swamp surface and ground water (from USFWS 1986b). 



53 



